The prolactin (PRL)-releasing activity of the novel prolactin-releasing peptides (PrRPs) was studied in vivo using male and lactating female rats. Whereas thyrotropin-releasing hormone effectively stimulated PRL and thyrotropin release as expected, PrRP in both animal models neither stimulated PRL secretion nor affected the release of other pituitary hormones. At the anterior pituitary level, in situ hybridization (ISH) histochemistry and Northern blot analysis revealed significantly higher expression levels of PrRP receptor (UHR-1) transcripts in female compared to male rats but not between lactating and nonlactating animals. By ISH, expression of UHR-1 mRNA was also detected in the intermediate lobe but not in the posterior pituitary. UHR-1 transcripts were also readily detectable in various hypothalamic brain areas whereas expression of PrRP mRNA was restricted to the ventral part of the dorsomedial hypothalamic nucleus but was not detected in neuroendocrine hypothalamic nuclei (e.g. PVN, SON). We thus assume that in the central nervous system, PrRP may likely have functions as a neuromodulator. However, together with the detailed cytochemical studies of various investigators that failed to detect PrRP-immunopositive nerve endings in the median eminence, our results strongly suggest that the hypothalamic PrRPs cannot be classified as hypophysiotrophic factors.

1.
Lamberts SW, Macleod RM: Regulation of prolactin secretion at the level of the lactotroph. Physiol Rev 1990;70:279–318.
2.
Ben-Jonathan N: Prolactin-releasing and inhibiting factors in the posterior pituitary. Neuroendocr Perspect 1990;8:1–38.
3.
Shin SH, Papas S, Obonsawin MC: Current status of the rat prolactin-releasing factor. Can J Physiol Pharmacol 1987;65:2036–2043.
4.
Dannies PS: A new releasing factor? With biotechnology and a little bit of luck. Endocrinology 1997;138:5085–5086.
5.
Hinuma S, Habata Y, Fujii R, Kawamata Y, Hosoya M, Fukusumi S, Kitada C, Masuo Y, Asano T, Matsumoto H, Sekiguchi M, Kurokawa T, Nishimura O, Onda H, Fujino M: A prolactin-releasing peptide in the brain. Nature 1998;393:272–276.
6.
Welch SK, O’Hara BF, Kilduff TS, Heller HC: Sequence and tissue distribution of a candidate G-coupled receptor cloned from rat hypothalamus. Biochem Biophys Res Commun 1995;209:606–613.
7.
Jacobs LS, Snyder PJ, Wilber JF, Utiger RD, Daughaday WH: Increased serum prolactin after administration of synthetic thyrotropin-releasing hormone in man. J Clin Endocrinol 1971;33:996–998.
8.
Tashjian AH, Barowsky NJ, Jensen DK: Thyrotropin-releasing hormone: Direct evidence for stimulation of prolactin production by pituitary cells in culture. Biochem Biophys Res Commun 1971;43:516–523.
9.
Neill JD: Neuroendocrine regulation of prolactin secretion; in Martini L, Ganong WF (eds): Frontiers in Neuroendocrinology. New York, Raven Press, 1980, vol 6, pp 129–156.
10.
Neill JD, Nagy GM: Prolactin secretion and its control; in Neill JD, Knobil E (eds): The Physiology of Reproduction. New York, Raven Press, 1988, vol 1, pp 1379–1390.
11.
Harms PG, Ojeda SR: A rapid and simple procedure for chronic cannulation of the rat jugular vein. J Appl Physiol 1974;36:391–392.
12.
Melton D, Krieg P, Rebagliati M, Maniatis T, Zinn K, Green MR: Efficient in vitro synthesis of biologically active RNA and RNA hybridization probes from plasmids containing a bacteriophage SP6 promoter. Nucleic Acids Res 1984;12:7035–7056.
13.
Angerer LM, Angerer C: In situ hybridization to cellular RNA with radiolabelled RNA probes; in Wilkinson DG (ed): In situ Hybridization. Oxford, IRL Press, 1992, pp 15–32.
14.
Samson WK, Resch ZT, Murphy TC, Chang JK: Gender-biased activity of the novel prolactin-releasing peptides. Endocrine 1998;9:289–291.
15.
De Léan A, Garon M, Kelly PA, Labrie F: Changes of pituitary thyrotropin-releasing hormone (TRH) receptor levels and prolactin response to TRH during the rat estrous cycle. Endocrinology 1997;100:1505–1510.
16.
De Léan A, Ferland L, Drouin J, Kelly PA, Labrie F: Modulation of pituitary thyrotropin-releasing hormone receptor levels by estrogens and thyroid hormones. Endocrinology 1997;100:1496–1504.
17.
Minami S, Nakata T, Tokita R, Onodera H, Imaki J: Cellular localization of prolactin-releasing peptide messenger RNA in the rat brain. Neurosci Lett 1999;266:73–75.
18.
Iijima N, Kataoka Y, Kakihara K, Bamba H, Tamada Y, Hayashi S, Matsuda T, Tanaka M, Honjyo H, Hosoya M, Hinuma S, Ibata Y: Cytochemical study of prolactin-relasing peptide in the rat brain. Neuroreport 1999;10:1713–1716.
19.
Thompson RH, Canteras NS, Swanson LW: Organization of projections from the dorsomedial nucleus of the hypothalamus: A PHA-L study in the rat. J Comp Neurol 1996;376:143–173.
20.
Bernardis LL, Bellinger LL: The dorsomedial hypothalamic nucleus revisited (1986 update). Brain Res Rev 1987;12:321–381.
21.
Chen CT, Dun SL, Dun NJ, Chang JK: Prolactin-releasing peptide immunoreactivity in A1 and A2 noradrenergic neurons of the rat medulla. Brain Res 1999;822:276–279.
22.
Yamakawa K, Kudo K, Kanba S, Arita J: Distribution of prolactin-releasing peptide-immunoreactive neurons in the rat hypothalamus. Neurosci Lett 1999;267:113–116.
23.
Maruyama M, Matsumoto H, Fujiwara K, Kitada C, Hinuma S, Onda H, Fujino M, Inoue K: Immunocytochemical localization of prolactin-releasing peptide in the rat brain. Endocrinology 1999;140:2326–2333.
24.
Matsumoto H, Murakami Y, Horikoshi Y, Noguchi J, Habata Y, Kitada C, Hinuma S, Onda H, Fujino M: Distribution and characterization of immunoreactive prolactin-releasing peptide in rat tissue and plasma. Biochem Biophys Res Commun 1999;257:264–268.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.